Histopathology and molecular biology of oligodendrogliomas

Abstract Historically, oligodendrogliomas have been defined morphologically as glial tumors marked by cells with rounded nuclei and scant cytoplasm. In the most recent revision to the World Health Organization classification of brain tumors, the definition of oligodendroglioma has been expanded to incorporate certain molecular findings, notably mutations in the isocitrate dehydrogenase genes (IDH) and deletions on chromosomes 1p and 19q. The purpose of this chapter is to review the classic morphologic features of oligodendrogliomas and to provide an overview of the key molecular pathologic findings utilized in clinical practice. This chapter will also consider morphologic differential diagnostic considerations including lesions such as diffuse astrocytoma, neurocytoma, dysembryoplastic neuroepithelial tumor and clear cell ependymoma, and discuss how to distinguish these look-alikes from oligodendrogliomas.